Transcript Meiosis: Plants

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SYNGAMY
gametes
zygote
germination
mitosis
differentiation
mitosis
gametangia
differentiation
Gametophyte1N
2N
Sporophyte
differentiation
differentiation
mitosis
germination
sporangium
mitosis
spores
sporocyte
MEIOSIS
The flowering plant is a multicellular diploid sporophyte.
The sporophyte encloses the multicellular haploid gametophyte.
The life history is thus diplohaplontic.
The gametes are oogamous but the sperm lack flagellae.
Gender expression has moved from gametophyte to sporophyte.
http://www.bakerlite.co.uk/pics/Wales/South%20Wales/Vale/Trees/Tree-8.jpg
Life Cycle of Flowering Plants Compare Fig. 41.2 Pg. 824
Compare Fig. 41.4a Pg. 826
Flower Organization-building a flower from the bottom up!
A flower is a short shoot (stem with leaves)
The stem is the receptacle with very short internodes
The leaves appear in four whorls
stigma
locule
ovule
flower hypogynous
gynoecium
flower
style carpel
perfect
anther
ovary
superior
pollen stamen
filament androecium
petal corolla
sepal
calyx
receptacle
pedicel
complete
perianth
Microsporogenesis: Prophase I of Meiosis
http://images.iasprr.org/lily/lpachy-m.jpg
Microsporogenesis: Late Prophase I of Meiosis
Synapsis: homologs join
Recombination: crossing over
http://images.iasprr.org/lily/lepto.jpg
Microsporogenesis: Metaphase I of Meiosis
http://images.iasprr.org/lily/meta-i.jpg
Microsporogenesis: Anaphase I of Meiosis
Centromeres do not breakdown
Homologs are separated: not sister chromatids
http://images.iasprr.org/lily/anaph.jpg
Microsporogenesis: Telophase I of Meiosis
Already haploid but
sister chromatids still joined
http://images.iasprr.org/lily/telo-i.jpg
Microsporogenesis: Metaphase II and Anaphase II of Meiosis
http://images.iasprr.org/lily/meta-ii.jpg
Microsporogenesis: Telophase II of Meiosis
http://images.iasprr.org/lily/telo-ii.jpg
Microsporogenesis: Meiosis complete (but prophase of mitosis)
http://images.iasprr.org/lily/tetrad.jpg
Microsporogenesis: Completed, Separated Microspores (note prophase)
http://images.iasprr.org/lily/microsp.jpg
Pollen Grain: Mitosis Makes Endosporic Microgametophyte
Pollen Wall: Microspore Wall (allergenic?)
Tube Cell
Generative Cell
Nucleus
Nucleus
Cytoplasm
Cytoplasm
The tube cell
digests a path
from the stigma
to the egg.
Compare Fig. 41.8
Pg. 829
The generative
cell follows the
path to the egg,
http://images.iasprr.org/lily/pollen2.jpg
and divides to
Pollination: vectormake two sperm
assisted movement of cells. Both
the pollen grain from the participate in
anther to the stigma.
syngamy.
Pollen Tube Growth
The tube cell germinates through the pollen wall.
The cell grows chemotropically toward the egg.
The pollen tube must find the ovule’s micropyle.
The generative cell slides along this tube.
It divides by mitosis to form two sperm cells.
http://bilbo.bio.purdue.edu/~cjslab/pollen-tubes.jpg
sperm
cells
SYNGAMY
gametes
zygote
germination
mitosis
differentiation
mitosis
gametangia
pollen
grain
tube cell
differentiation
Gametophyte1N
2N
Sporophyte
differentiation
differentiation
mitosis
germination
sporangium
mitosis
spores
sporocyte
MEIOSIS
generative cell
anther
microspore
The large plant is a sporophyte.
Its flower produces the sporangia; on the male side, the anther of the stamen
The anther contains sporocytes that divide by meiosis to make spores
The spore cell divides to make an endosporic microgametophyte… a pollen grain
The tube cell digests a path to the egg
The generative cell divides into two sperm cells that participate in syngamy
http://www.bakerlite.co.uk/pics/Wales/South%20Wales/Vale/Trees/Tree-8.jpg
Life Cycle of Flowering Plants
Compare Fig. 41.4a Pg. 826
Flower Organization
Now we focus on what is happening on the female side…
We will examine what is going on inside the ovule of the carpel.
stigma
locule
ovule
flower hypogynous
gynoecium
flower
style carpel
perfect
anther
ovary
superior
pollen stamen
filament androecium
petal corolla
sepal
calyx
receptacle
pedicel
complete
perianth
Alstroemeria: What is different two weeks later?
Bisexual
…but functionally unisexual
…by being trans-sexual
protandrous:
first-male
protogynous:
first-female
(antonym)
Megasporogenesis: taking place inside the ovule inside the ovary.
megasporocyte
meiosis I
4 megaspores
meiosis II
3 disintegrate
functional
megaspore
mitotic divisions without cytokinesis megagametophyte
3 antipodals
central cell
cytokinesis
egg
2 synergids
Compare Fig. 41.7 Pg. 828
and Fig. 41.11 Pg. 832
central cell
egg
embryo sac
SYNGAMY
gametes
zygote
germination
mitosis
differentiation
mitosis
gametangia
differentiation
Gametophyte1N
antipodals
2N
Sporophyte
differentiation
differentiation
mitosis
germination
sporangium
mitosis
spores
sporocyte
ovule
MEIOSISmegasporocyte
synergids
http://www.bakerlite.co.uk/pics/Wales/South%20Wales/Vale/Trees/Tree-8.jpg
Life Cycle of Flowering Plants
The large plant is a sporophyte.
Its flower produces the sporangia; on the female side, the ovule of the carpel
The ovule contains a megasporocyte that divides by meiosis to make four megaspores
Three megaspores disintegrate.
The remaining megaspore cell divides by mitosis to make 8 nuclei.
Cytokinesis divides the 8 nuclei into seven cells of the megagametophyte (embryo sac)
The egg cell and the central cell are gametes that fuse with two sperm cells in syngamy
The ovule, with zygotic embryo and triploid endosperm, becomes a seed.
Compare Fig. 41.11 Pg. 832
In Flowering Plants, syngamy is a double event:
syngamy#2:
sperm
nuclei
2 x 1N polar nuclei + 1N sperm
= 3N primary endosperm cell
no miracle-grow, no compost!
syngamy#1:
1N egg + 1N sperm = 2N zygote
synergids
disintegrating
http://botit.botany.wisc.edu/courses/img/Botany_
130/Diversity/Angiosperms/Fertilization.jpg
In this slide, plasmogamy has
already occurred…but what
part of syngamy has not
occurred yet? karyogamy!